The present invention relates to an infrared communication system, and particularly to a wireless system including a plurality of relay units for receiving and transmitting infrared signals through free air.
Infrared communication systems commonly include optical fibers for establishing communication between various terminals of the system. However, there are many situations wherein it is desirable to connect the various terminals in a fiberless manner, i.e., via free air and not via optical fibers. The ability of one terminal, in a fiberless infrared communication system, to correctly intercept a message transmitted by another terminal depends on receiver dependent factors, transmitter dependent factors, and medium dependent factors. The receiver dependent factors include, among others, the sensitivity and radiation acceptance angle of the receiver. The transmitter dependent factors include, among others, the radiation intensity and the radiation pattern. The medium (and system) dependent factors include, among others, the distance between the receiver and the transmitter, the position (stationary or dynamic) of one relative to the other, the presence or absence of a line of sight between the two, obstructions in the path of the radiation, and reflections suffered by the radiated signal in its way to the receiver.
A typical infrared communication system includes infrared LEDs (light-emitting diodes) as emitters, and photodiodes as receptors. However, generally such emitters and receptors have disadvantageous characteristics particularly when used in a fiberless (i.e., through free air) infrared communication system, such as limited emission-reception angles, limited switching speed, and high power demands. These disadvantageous characteristics make the use of conventional emitters and receptors of the foregoing type impractical in many or most cases for portable, reliable, and relatively inexpensive fiberless infrared communication systems.